110 lines
3.4 KiB
Markdown
110 lines
3.4 KiB
Markdown
[map.access]
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# 23 Containers library [[containers]](./#containers)
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## 23.4 Associative containers [[associative]](associative#map.access)
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### 23.4.3 Class template map [[map]](map#access)
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#### 23.4.3.3 Element access [map.access]
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[ð](#lib:operator%5b%5d,map)
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`constexpr mapped_type& operator[](const key_type& x);
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`
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11815)
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*Effects*: Equivalent to: return try_emplace(x).first->second;
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[ð](#lib:operator%5b%5d,map_)
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`constexpr mapped_type& operator[](key_type&& x);
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`
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11826)
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*Effects*: Equivalent to: return try_emplace(std::move(x)).first->second;
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[ð](#lib:operator%5b%5d,map__)
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`template<class K> constexpr mapped_type& operator[](K&& x);
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`
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11837)
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*Constraints*: The [*qualified-id*](expr.prim.id.qual#nt:qualified-id "7.5.5.3 Qualified names [expr.prim.id.qual]") Compare::is_transparent is valid and denotes a type[.](#3.sentence-1)
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11842)
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*Effects*: Equivalent to: return try_emplace(std::forward<K>(x)).first->second;
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[ð](#lib:at,map)
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`constexpr mapped_type& at(const key_type& x);
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constexpr const mapped_type& at(const key_type& x) const;
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`
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11854)
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*Returns*: A reference to the mapped_type corresponding to x in *this[.](#5.sentence-1)
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[6](#6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11858)
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*Throws*: An exception object of type out_of_range if
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no such element is present[.](#6.sentence-1)
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[7](#7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11863)
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*Complexity*: Logarithmic[.](#7.sentence-1)
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[ð](#lib:at,map_)
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`template<class K> constexpr mapped_type& at(const K& x);
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template<class K> constexpr const mapped_type& at(const K& x) const;
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`
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[8](#8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11875)
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*Constraints*: The [*qualified-id*](expr.prim.id.qual#nt:qualified-id "7.5.5.3 Qualified names [expr.prim.id.qual]") Compare::is_transparent is valid and denotes a type[.](#8.sentence-1)
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[9](#9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11880)
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*Preconditions*: The expression find(x) is well-formed and has well-defined behavior[.](#9.sentence-1)
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[10](#10)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11884)
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*Returns*: A reference to find(x)->second[.](#10.sentence-1)
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[11](#11)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11888)
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*Throws*: An exception object of type out_of_range iffind(x) == end() is true[.](#11.sentence-1)
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[12](#12)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11893)
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*Complexity*: Logarithmic[.](#12.sentence-1)
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